Subject: Re: [PATCH] powerpc/book3s_hv_uvmem: Check for failed page migration

From: Alistair Popple <[email-masked]>
Date: Mon, 07 Dec 2020 11:13:58 +1100

On Saturday, 5 December 2020 3:52:44 AM AEDT Ram Pai wrote:
> On Fri, Dec 04, 2020 at 03:48:41PM +0530, Bharata B Rao wrote:
> > On Thu, Dec 03, 2020 at 04:08:12PM +1100, Alistair Popple wrote:

> This patch certainly looks like the problem, that has been hurting
> us for a while.  Let me run this patch through my SVM tests.  Looks very
> promising.
> 
> BTW: The code does a similar thing while paging out.  It pages out from the
> UV, and then does the migration. Is there a bug there aswell?

As specified the migrate_pages_vma() API can fail to migrate device private 
pages. However the fix was less obvious to me, and in practice I don't think it 
will ever fail for device private pages as you don't have the same races to 
establish the page and device private pages can't be pinned.

It might be worth adding some kind of warning though in case this ever 
changes.

 - Alistair
 
> RP